A powered device is configured to displace its position by means of a motor. For example, JP2007-62507A (hereinafter referred to as Patent reference 1) discloses an electric driven seat apparatus for a vehicle, which is configured to switch a seatable state where an occupant is seatable and a stored state where a usable space in a vehicle is expanded by motors. According to the seat apparatus disclosed in Patent reference 1, the seatable state and the stored state are switched by an operation of a switch by the occupant. A seat cushion and a seatback are actuated by each of the motors while the occupant maintains the operation of the switch to switch the seatable state and the stored state.
During the switching operations between the seatable state and the stored state, there is a possibility that the seat cushion and the seatback entrap a part of the occupant's body, occupant's clothes, and other objects. In order to overcome this drawback, a motor control device includes a detection means for detecting an entrapment and/or a safety shutdown means. JP2008-136325A (hereinafter referred to as Patent reference 2) discloses a motor drive apparatus which includes a detection means for detecting an entrapment. In a case where a seatback is moved from a reclining position to an upright position, a frictional resistance may be generated between lateral surfaces of adjacent seatbacks, and the fictional resistance may be detected as an entrapment. For example, in a case where the apparatus detects the entrapment using a pulse obtained from a rotation sensor detecting a motor rotation, the apparatus may erroneously detect that the entrapment is caused when a pulse width is expanded due to the frictional resistance. In order to overcome this drawback, the motor drive apparatus disclosed in Patent reference 2 detects whether the entrapment is caused based on whether a value obtained by integrating variation of pulse cycle obtained from the rotation sensor exceeds a predetermined threshold value or not.
For example, in a case where a frictional resistance is generated between the lateral surfaces of the adjacent seatbacks, a load suddenly increases thereby increasing a length of a pulse cycle on a short-term basis. That is, a change rate of the pulse cycle surges. On the other hand, in a case where an entrapment is caused, a level of the load is gradually increased to gradually increase the length of the pulse cycle. In other words, the change rate of the pulse cycle gradually increases. According to Patent reference 2, an integrated value of ratios between one pulse cycle and a next pulse cycle (i.e., variation) of 150 cycles (i.e., 150 when there is no change) is obtained. In a case where the frictional resistance is generated between the lateral surfaces of the adjacent seatbacks, because the length of the pulse cycle is increased on the short-term basis, the maximum value of an integrated value of ratios between one pulse cycle and a next pulse cycle is assumed to be smaller than the case where the entrapment is caused in a long-term corresponding to 150 cycles. Accordingly, an erroneous detection of the entrapment is restrained by performing the detection of the entrapment based on the level of the integrated value and detects the entrapment when the integrated value exceeds the predetermined threshold value.
In a case where mechanical end points are provided within a movable range of a movable portion, for example, a case of vehicle seat, if a seat (seat cushion, or seatback) reaches the end point while the motor is steadily rotating, an impact noise and an uneasy vibration may be generated when the seat (seat cushion, or seatback) mechanically stops at the end point. Accordingly, a rotation speed of the motor may be gradually decreased when the seat (seat cushion, or seatback) comes to be in the vicinity of the end point so as to stop slowly. Similarly, in a case where the motor is actuated with a steady rotation speed immediately after starting operation of the seat (seat cushion, or seatback), the seat (seat cushion, or seatback) may be suddenly moved or an excessive load may be applied to the motor. Accordingly, the seat (seat cushion, or seatback) may be moved slowly at a start by gradually increasing the motor rotation speed. When the seat (seat cushion, or seatback) is controlled to start moving slowly or to stop slowly, pulse cycles obtained from the rotation sensor are varied. Thus, the application of disclosure in Patent reference 2 is not appropriate in case of controlling the rotation speed of the motor to gradually increase or gradually decrease. The entrapment could be detected by detecting that the length of the pulse cycle is increased during a constant speed operation or an accelerating operation of the motor with the construction disclosed in Patent reference 2. However, in a case where the motor is controlled to decrease the rotation speed, it is difficult to distinguish whether the length of the pulse cycle is decreased because of the speed reduction of the motor rotation or because of the entrapment of a part of an occupant's body, occupant's clothes, or other objects. Thus, a precision of the detection of the entrapment may be decreased.
A need thus exists for a motor control device and a seat control device which is not susceptible to the drawback mentioned above.